Genetic epidemiology, the union of human genetics and epidemiology, is a rapidly expanding field which is becoming more prominent as the complexity of the genetic and environmental interactions affecting human traits has been gaining wider recognition. A group of genetic epidimiologists now exists at Yale University in the Department of Human Genetics, Department of Epidemiology and Public Health, and the Child Study Center. The three faculty members specializing in this area (Kidd, Risch, and Pauls) with their students and postdoctoral fellows ar involved in many different collaborations. The data analyses by this research group make enormous demands on computer resources, especially central processor (CPU) time. The size of the group, the numerous analyses of the many large and expanding datasets, and the ongoing development of even more sophisticated analytic methods and computer programs have saturated the computer resources available at Yale. Some important work has already had to be postponed due to the growing demand for limited computer resources. To continue the research of this highly productive group at the same level and to meet its growing needs, additinal computer resources must be obtained. After considerable thought and evaluation a small mainframe computer, specifically an IBM 4361 Model 5, appears to be the most cost effective means of satisfying the antaicipated computer needs over the next three to five years. This application proposes the purchase of such a machine.